bug#18006: Simplify via set_binary_mode

[Eli Zaretskii <eliz@gnu.org>]

> Date: Mon, 14 Jul 2014 13:16:06 -0700
> From: Paul Eggert <eggert@cs.ucla.edu>
> CC: 18006@debbugs.gnu.org
> 
> Your explanation of _fmode led me to find a minor porting bug. 
> Fx_load_color_file [!HAVE_X_WINDOWS] uses fopen with "rt"; unlike "rb" 
> this isn't specified by POSIX and a web search suggests that it does 
> fail on a few older platforms.  Emacs no longer modifies _fmode so "r" 
> should suffice now anyway.  Also, there are two other places where some 
> "rt"-related simplifications can be done.  Proposed further patch attached.

Thanks.  The lib-src part looks OK to me.

> --- src/ChangeLog	2014-07-14 19:23:18 +0000
> +++ src/ChangeLog	2014-07-14 19:46:54 +0000
> @@ -1,5 +1,10 @@
>  2014-07-14  Paul Eggert  <eggert@cs.ucla.edu>
>  
> +	Use "b" flag more consistently; avoid "t" (Bug#18006).
> +	* lread.c (Fload) [DOS_NT]:
> +	* xfaces.c (Fx_load_color_file) [!HAVE_X_WINDOWS]:
> +	No longer need to use "rt" instead of "r".

This part doesn't look right.  If we don't use "rt", then when
emacs_fopen calls emacs_open, the latter will interpret the lack of
"t" as a sign to use the default binary mode, which is not what we
want.

I think we can fix this in one of 2 ways: either (a) let emacs_fopen
start with O_TEXT in bmode by default, at least on DOS_NT platforms;
or (b) change emacs_open back to not apply O_BINARY by default, and
instead use "rb", "wb", and O_BINARY in all the places except those
that use "rt" or "wt" now.

I like the latter alternative better, because the former makes
emacs_fopen and emacs_open use 2 different defaults (text vs binary),
which is contrary to intuition and easy to forget.

WDYT?